Message-ID: <4E40B08C.6010309@2ndquadrant.com>
Date: Mon, 08 Aug 2011 23:59:08 -0400
From: Greg Smith <greg@2ndquadrant.com>
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To: Kevin Grittner <Kevin.Grittner@wicourts.gov>
CC: pgsql-performance@postgresql.org, Claire Chang <yenhsiac@yahoo.com>
Subject: Re: Postgres 8.4 memory related parameters
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Kevin Grittner wrote:
> Claire Chang <yenhsiac@yahoo.com> wrote: 
>   
>> shared_buffers = 32GB
>>     
>  
> I seem to remember seeing some benchmarks showing that performance
> falls off after 10GB or 20GB on that setting.
>   

Not even quite that high.  I've never heard of a setting over 10GB being 
anything other than worse than a smaller setting, and that was on 
Solaris.  At this point I never consider a value over 8GB, and even that 
needs to be carefully matched against how heavy the writes on the server 
are.  You just can't set shared_buffers to a huge value in PostgreSQL 
yet, and "huge" means ">8GB" right now.

Note that the problems you can run into with too much buffer cache are 
much worse with a low setting for checkpoint_segments...and this 
configuration doesn't change it at all from the tiny default.  That 
should go to at least 64 on a server this size.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us